Synthesis and structure of Pt(II) phosphonato-phosphine complexes and of a P,O-stabilized metal-metal-bonded Pt2Ag2 complex

As part of our interest in the design and reactivity of P,O ligands, and because the insertion chemistry of small molecules into a metal alkyl bond is very dependent on the ancillary ligands, the behavior of Pt-methyl complexes containing the beta-phosphonato-phosphine ligand rac-Ph2PCH(Ph)P(0)(OEt)(2) (abbreviated PPO in the following) toward CO insertion has been explored. New, mononuclear Pt(II) complexes containing one or two PPO ligands, [PtClMe-(kappa(2)-PPO)] (1), [Pt{C(O)Me}Cl(kappa(2)-PPO)] (2), [PtMe(CO)(kappa(2)-PPO)]OTf (3.OTf), [PtMe(OTf)(kappa(2)-PPO)] (4), trans-[PtClMe-(kappa(1) -PPO)2] (5), [PtMe(kappa(2)-PPO)(kappa(1)-PPO)]BF4 (6.BF4), [PtMe(kappa(2)-PPO)(kappa(1)-PPO)OTf (6.OTf), and [Pt{C(O)Me}(K-2-PPO)(K-1-PPO)]BF4 (7.BF4) have been prepared and characterized. Hemilability of the ligands is observed in the cations 6 and 7 in which the terminally bound and chelating PPO ligands exchange their role on the NMR time-scale. The acetyl complexes 2 and 7 are stable in solution, but the former deinserts CO upon chloride abstraction. We also demonstrate the ability of PPO to behave as an assembling ligand and to stabilize a heterometallic Pt-Ag metal complex, [PtMe(kappa(2)-PPO) {mu-(eta(1)-P:eta(1)-O)PPO)}Ag(OTf)(Pt-Ag)]OTf (B.OTf), which was obtained by reaction of 5 with AgOTf to generate more reactive, cationic complexes. Whereas the first equivalent of AgOTf abstracted the chloride ligand, the second equivalent added to the cationic complex with formation of a Pt-Ag bond (2.819(1) Angstrom). The complexes 1, 2, 4, 5-CH2Cl2, and (8-OTf)(2) have been structurally characterized by single-crystal X-ray diffraction. The latter has a dimeric nature in the solid state, with two silver-bound triflates acting as bridging ligands between two Pt-Ag moieties. In addition to the Ag-Pt bond, the Ag cation is stabilized by a dative O --> Ag interaction involving one of the PPO ligands.